Recently, a spacer prepared from a photosensitive resin composition is employed in order to maintain a constant distance between the upper and lower transparent substrates in liquid crystal cells of a liquid crystal display (LCD). In an LCD, which is an electro-optical device driven by a voltage applied to a liquid crystal material injected into a constant gap between two transparent substrates, it is very critical to maintain the gap between the two substrates to be constant. If there is an area in which the gap between the transparent substrates is not constant, the voltage applied thereto as well as the transmittance of light penetrating this area may vary, resulting in a defect of spatially non-uniform luminance. According to a recent demand for large LCD panels, it is even more critical to maintain a constant gap between two transparent substrates in an LCD.
Such a spacer may be prepared by coating a photosensitive resin composition onto a substrate and exposing the coated substrate to ultraviolet rays and so on with a mask placed thereon, followed by development thereof. Recently, efforts of using a light shielding material for a spacer have been made; accordingly, various colored photosensitive resin compositions have been actively developed.
In recent years, a black column spacer (BCS) in which a column spacer and a black matrix are integrated into a single module using a colored photosensitive resin composition has been aimed to simplify the process steps. The colored photosensitive resin composition used in the production of such a black column spacer is required to easily form a step difference and a pattern in a high resolution.
In the meantime, if a cured film has uneven wrinkles on its surface when a bezel is formed in a display panel from a colored photosensitive resin composition, it may cause a serious disadvantage that the amount of injected liquid crystals may not be uniform due to a defect in the gap between the upper and lower plates during their assembly or that spots may be generated on the edges of the display screen due to a poor transmission of electric signals.
In addition, when a light shielding spacer and a cured film are prepared from the colored photosensitive resin composition as mentioned above, it is necessary to have a peculiar transmittance at a specific wavelength band to facilitate the progress of the process and to prevent a light blurring phenomenon of red or green color that may be caused by the backlight emitting from the rear side of the panel after the formation of a pattern and a cured film.
In order to suppress the generation of wrinkles on the surface of a cured film, therefore, a photosensitive resin composition comprising an acrylic resin as a wrinkle generation inhibitor has been proposed (Korean Patent No. 1291480). In Korean Patent No. 1291480, however, since the acrylic resin thus employed comprises (meth)acrylic acid units in a large amount of 60 to 85% by mole, it is difficult to form a step difference of a pattern for preparing a light shielding spacer due to such a high acid value of the acrylic binder.